Prostaglandin D (hereinafter referred to as “PGD”) are known as a metabolite in the arachidonic acid cascade, and are known to have effects of bronchoconstriction, vasodilatation or vasoconstriction and platelet aggregation inhibition. PGD is considered to be produced from mast cells, and the increase of PGD concentration has been recognized among systemic mastocytosis patients (New Eng. J. Med., 303, 1400–1404 (1980)). Also, PGD is considered to relate to neuro activities, especially, sleep and hormone secretion. Furthermore, there are reports suggesting participations in platelet aggregation, glycogen metabolism, ocular tension adjustment and the like.
PGD shows its effects by binding to a DP receptor which is a receptor thereof. A DP receptor antagonist binds to and is antagonistic to its receptor so that it can inhibit the function of PGD. Accordingly, it is considered to be useful for the prevention and/or treatment of diseases, for example, allergic diseases such as allergic rhinitis, allergic conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, etc.; systemic mastocytosis; disorders due to systemic mastocyte activation; anaphylactic shock; bronchoconstriction; urticaria; eczema; allergic bronchopulmonary aspergillosis; inflammatory paranasal sinus; nasal polyp; hypersensitive angitis; eosinophilia; contact dermatitis; diseases accompanied with itching, such as atopic dermatitis, urticaria, allergic conjunctivitis, allergic rhinitis, contact dermatitis, etc.; secondary diseases caused by behaviors (scratching behaviors, beating, etc.), such as cataract, retinal detachment, inflammation, infection, sleep disorder, etc.; inflammation; chronic obstructive pulmonary disease; ischemic reperfusion disorder; cerebrovascular disorder; pleuritis complicated by rheumatoid arthritis; ulcerative colitis; and the like. Moreover, it is considered to relate to sleeping and platelet aggregation and to be useful for these diseases.
Some DP receptor antagonists are known until now, and BW-A868C represented by formula (A) is considered to be the most selective:

Also, recently, DP receptor antagonists which are thromboxane derivatives have been published in WO 98/25915, WO 98/25919, WO 97/00853, WO 98/15502 and the like.
On the other hand, as a compound similar to the compound of the present invention, an indole compound represented by formula (B) is known as a synthetic intermediate (J. Heterocyclic Chem., 19, 1195 (1982)).
